This application is based on Japanese patent applications No. 8-288857 filed on Oct. 30, 1996, and No. 8-288858 filed on Oct. 30, 1996, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a solid state image pickup device, and more particularly to the structure of a solid state image pickup device suitable for realizing high resolution and capable of reading pixel signals of one frame at the same time.
b) Description of the Related Art
Charge transfer type solid state image pickup devices or so-called charge coupled devices (CCD) have been developed to mount them on cameras of televisions, video tape recorders and the like of NTSC standards. In NTSC standards, an image of one frame is divided into signals of two fields through interlace scanning, and signal charges of photosensors of the first or second field are read at the same time. In other words, two photosensors are generally provided with one transfer stage.
Non-interlace scanning is necessary, however, for electronic still cameras or televisions of new standards. In this case, one photosensor is provided with one transfer stage (generally four electrodes). As a method of configuring this structure, a solid state image pickup device having the structure shown in FIG. 9 has been proposed.
FIG. 10 is a schematic plan view showing at a larger scale a partial area of a solid image pickup device of the non-interlace type that signals of all pixels of one frame can be read at the same time. In FIG. 10, reference numeral 1 represents a photoelectric conversion element (hereinafter called a photosensor) such as a photodiode. Photosensors 1 generally indicated at 2a and disposed in the vertical direction (column direction) as viewed in FIG. 10 constitute a first photosensor column. Photosensors 1 generally indicated at 2b and disposed in the vertical or column direction constitute a second photosensor column. The first and second photosensor columns 2a and 2b are alternately juxtaposed in the right/left direction (row direction) as viewed in FIG. 10. Photosensors 1 generally indicated at 3 and disposed in the row direction constitute a first photosensor row. Photosensors 1 generally indicated at 4 and disposed in the row direction constitute a second photosensor row. The first and second photosensor rows 3 and 4 are alternately disposed side by side in the column direction.
In FIG. 10, reference numerals 5 and 6 represent first and second column direction charge transfer devices for reading signal charges of the first and second photosensor columns 2a and 2b and transferring the read charges in the column direction. In other words, the first and second column direction charge transfer devices are disposed on both sides of each photosensor column to receive signal charges from every second photosensors and transfer them in the column direction.
Also in FIG. 10, reference numeral 7 represents a controller (gate) for controlling to select signal charges transferred by either the first or second column direction charge transfer device 5, 6 and transfer the selected signal charges to a row direction charge transfer device 8 which transfers the received signal charges in the row direction. Reference numeral 9 represents an output circuit (amplifier) for generating voltages corresponding to the amounts of signal charges transferred from the row direction charge transfer device 8 and outputting the generated voltages to an external circuit (not shown). The photosensors 1, column direction charge transfer devices 5 and 6, controllers 7, row direction charge transfer device 8 and output circuit 9 are all integrally formed on a single semiconductor substrate (not shown).
In the above-described solid state image pickup device shown in FIG. 10, the first and second column direction charge transfer devices 5 and 6 are disposed on both sides of each photosensor column 2a, 2b and provide one transfer stage 150 per one photosensor 1. Each transfer stage 150 includes charge signal storage regions (packets).
Solid state image pickup devices used with electronic still cameras or television cameras of new standards are desired to have the same pitch of photosensors both in the row and column directions. If the pitch of photosensors is same in both the row and column directions, photosensors can be disposed in a square lattice shape. This layout is advantageous in that the pitch of pixels of a display device has integrity with that of photosensors of the solid state image pickup device and in that signal processing becomes easy.
However, since two column direction charge transfer devices 5 and 6 are disposed between the first and second photosensor columns 2a and 2b, the pitch Wh of photosensors disposed in the row direction is longer than that Wv of photosensors disposed in the column direction, and it is difficult to shorten the pitch in the row direction. In order to make both the pitches equal, the pitch in the column direction is required to be broadened to the pitch in the row direction. This approach, however, results in difficulty in high integration of solid state image pickup devices.
Further, in the structure shown in FIG. 10, the direction of reading signal charges of photosensors in each row by the first column charge transfer device 5 is opposite to that by the second column charge transfer device 6. If the relative position of the photosensor columns 2a and 2b and the first and second column direction charge transfer devices 5 and 6 is displaced during the manufacture processes of solid state image pickup devices, the characteristics of reading pixel signals change between adjacent photosensors disposed in the row direction. For example, if the photosensors 1 are displaced to the right relative to the column direction charge transfer devices 5 and 6, the relative position of the photosensors 1 constituting the first photosensor row 3 and the first column transfer device 5 becomes short whereas the relative position of the photosensors 1 constituting the second photosensor row 4 and the second column transfer device 6 becomes long. Therefore, signal charges of the first photosensor row 3 are easy to read, whereas signal charges of the second photosensor row 4 are difficult to read.
Still further, since the amounts of false signals called smear become different between the first and second column direction charge transfer devices 5 and 6, a fatal fixed pattern in a vertical strip shape appears as noises. Smear is generated by the leakage of a fraction of light incident upon the photosensor 1 to the column direction charge transfer devices 5 and 6.
In the structure of such a conventional solid state image pickup device, the pitch in the row direction from the first column direction charge transfer device 5 to the second transfer device 6 interposing an element separation layer 10 therebetween is different from the pitch from the second transfer device 6 to the first transfer device 5 interposing each photosensor 1 therebetween. For the coupling of charge signals between the first and second column direction charge transfer devices 5 and 6 to the row direction charge transfer device 8, it becomes necessary to make the pitch of all the first and second column direction charge transfer devices 5 and 6 equal to that of all transfer stages of the row direction charger transfer device 8. To this end, the controller 7 is provided between the column direction charge transfer device 5, 6 and the row direction charge transfer device 8, so as to substantially combine two adjacent first and second column direction charge transfer devices 5 and 6 and couple a combined set of two transfer devices 5 and 6 to the row direction charge transfer device 8. However, in this case, in transferring all signal charges of one row in the column direction, two complicated transfer operations are required. Namely, each controller 7 performs a first transfer operation for transferring signal charges from the first column direction charge transfer device 5, and then a second transfer operation for transferring signal charges from the second column direction charge transfer device 6.
It is an object of the present invention to provide a solid state image pickup device with a novel structure capable of improving a resolution and realizing uniform characteristics of photosensors in each row even if conventional manufacture processes are used.
According to one aspect of the present invention, there is provided a solid state image pickup device comprising:
a plurality of photoelectric conversion element pairs disposed in a row direction and a column direction, each pair constituting one unit including two adjacent photoelectric conversion elements disposed in the column direction, wherein a pitch of pairs in the row direction is generally equal to a pitch of pairs in the column direction.
According to another aspect of the present invention, there is provided a solid state image pickup device comprising: a plurality of photoelectric conversion elements disposed in a row direction and a column direction at a predetermined pitch; first and second column direction charge transfer devices disposed on both sides of each photoelectric conversion element column including a plurality of photoelectric conversion elements disposed in the column direction, the first and second column direction charge transfer devices transferring signal charges output from the photoelectric conversion elements in the column direction; a row direction charge transfer device for transferring signal charges in the row direction; a channel position changing unit for transferring signal charges from the first and second column direction charge transfer devices to the row direction charge transfer device, the channel position changing unit adjusting positions of all signal charges from the first and second column direction charge transfer devices to be at a constant interval on the row direction charge transfer device; and an output circuit for converting signal charges from the row direction charge transfer device into voltage signals and outputting the voltage signals.
A solid state image pickup device having uniform characteristics of photosensors in each row, of the type that signal charges of all pixels in one frame are read at the same time, can be realized without forming photoelectrically inactive areas, by using conventional manufacture processes of a solid image pickup device with two-layer stacked electrodes with partially overlapped regions. Furthermore, the pitch of photosensor pairs in the column direction is made generally equal to that of photosensors in the row direction. Accordingly, the resolution of the solid state image pickup device can be improved without broadening the pitch of photosensors.